Prevention of cracks in cylinder heads



Nov. 8, 1955 R. H. SHEPPARD PREVENTION OF CRACKS IN CYLINDER HEADS 2Sheets-Sheet 1 Filed Nov. 10, 1954 :orIs:

IN VEN TOR.

Nov. 8, 1955 R. H. SHEPPARD 2,722,922

PREVENTION OF CRACKS IN CYLINDER HEADS Filed Nov. 10, 1954 2Sheets-Sheet 2 FIG. 2

United States Patent Urifice 2,722,922 Patented Nov. 8, 1955 PREVENTIONOF CRACKS IN CYLINDER HEADS Richard H. Sheppard, Hanover, Pa.Application November 10, 1954, Serial No. 467,965

3 Claims. (Cl. l2341.74)

This invention relates to internal combustion engines of the type havingrathernarrow metal bridges extending between the thick sections of acylinder head, which are required because of the high pressure usual insuch engines particularly those of the diesel type. The principal objectof the present invention is to retard the cumulative crack-formingeffect of the alternate expansion and contraction of these bridges asthey are compressed lengthwise during the warm-up periods and are placedin tension in the cooling off periods by the surrounding masses of therelatively thick sections which they connect.

A further object of the invention is to provide for the passage of waternot only through the metal between the proximate valve seat inserts of acylinder head but also between the combustion chamber of a valve in headDiesel engine and each of the two adjacent valve seat inserts, thisbeing particularly advantageous in engines having the larger size boresas the tendency of this metal to form cracks constantly growing inlength and depth, seems to increase at a geometrical rate with increaseof diameter as the bore diameter exceeds about 3 /2". By equalizing thetemperature in these three bridging members, distortion of the valveseat inserts is also lessened to a degree that permits an appreciablesaving in labor costs in the grinding of the valves.

In the drawings:

Figure 1 is a plan view of a portion of a cylinder head;

Figure 2 is a transverse vertical section through a combustion chamberrecess;

Figure 3 is a vertical section on line 3--3 of Figure 1;

Figure 4 is a side elevation.

Referring first to Figure 2, the cylinder head casting has a top wallfrom which extends downwardly a boss 11 having a circular hole 12 to fitthe body of an injector which engages the threads 14 so that theinjector snugly fits the holes 12 and 15 and thus prevents water fromthe spaces 17 and 18 entering this area. The large recess 20, coaxialwith threads 14 and the holes 12, 15 and 21, receives the usualcombustion chamber insert. A bore 25 is drilled from the flat side face26 of the casting to a point such as 27 fairly close to the recess andslightly farther from the face 28 which engages the engine block thanfrom the usual bottom or flow 29 of the water space. A small ridge 30 isprovided above the drilled bore to provide suflicient metal directlyabove the bore.

In previous practice a hole was drilled through the upper face 33 of thecasting so as to make a vertical bore in the bridge 35 between theintake and exhaust recesses 37 and 38 respectively, water being admittedto the bore 25 through a short bore 39 drilled through the bottom face28 of the casting. This was perfectly satisfactory for engines havingsmaller bores and has proved highly advantageous for engines of thissize but when we come to engines having bores of about 4%" it becomesnecessary to provide for temperature equalization between the combustionchamber recess 20 and each of the two proximate valve recesses 27 and 28for all loads above 1800 as well as for overloads at that figure. For aslightly larger bore, say 4 /2", unless there is thermal control in thebridges on both sides of the combustion chamber recess, there will bedanger of the formation of cumulative cracks at speeds exceeding 1600.

It is believed that cracks are formed in absence of the bores of thepresent invention by reason of the rapid rise in temperature of thenarrow bridges during the warm-up period this being particularly trueduring cold weather. The massive portions of the casting heat up veryslowly whereas the small narrow bridges heat rapidly being at thehottest part in the entire casting and consequently all three of thebridges tend to expand lengthwise quite quickly and long before theother portions of the casting have come up to operating temperature.

The cracking is minimized by warming the engine up slowly and being surethat the heat is fairly uniformly distributed before a heavy load isapplied. Equally obviously, it is very difficult to teach the ordinaryoperator to take this much care with the engine. Tendency to crack isincreased greatly by high speeds and heavy loads. Almost exactly thesame trouble is encountered when the engine is stopped. The cylinderhead cools down slowly especially in the thicker portions and since thethree bridges are both narrow and short and are surrounded by masses ofiron of much greater strength because of their sizes, the tendency tocrack or to increase cracks already formed is greatly increased.

By joining the bore 25 by additional passageways drilled from the sideface 40 opposite the face 26 and locating these additional boressubstantially at right angles to each other and about in the center ofthe bridges 40 and 41 and with direct communication above at someconvenient point with the water space in the head directly above theadditional bores, the desired temperature control is obtained.

As a typical example: bores 50 and 51 are drilled from points 52 and 53in the face 40 so that the axes of the three bores 25, 50 and 51 all liein the same horizontal plane, assuming the bottom face 28 to behorizontal. These bores are continued until they intersect at point 55with bore 25. The critical areas may then be maintained at such atemperature as to minimize the formation of cracks caused by thealternate compression and tension in the metal. All three of the boresare closed at their entry ends by plugs 56, 57 and 58. The verticalshort bores 59 and 60 lead vertically down from the water space in thehead to the slanting bores well beyond any critical point. There is thusbuilt up a slight pressure differential between the engine block (notshown) and the cylinder head which pressure aids in overcoming thefriction of the three long drilled passages.

In operation, water from the engine block (not shown) enters through thevertical short passage 39, travels along bore 25 which is the stem of aY and on reaching point 50 and 51 discharging 55 branches evenly intobores from each through the short vertical bores 59 and 60 to the mainwater space in the head. By carrying heat from the three narrow bridgesbetween the combustion chamber and the valve inserts and between theinserts during the warm-up period and by delaying the cooling of thesebridges during the cooling off period, the formation of thermal cracksis minimized if not prevented.

What I claim is:

l. A cylinder head casting having therein recesses for a combustionchamber, an exhaust valve and an inlet valve, with bridges of metalextending in Y formation between the three recesses and joining thebottom wall of the casting, characterized by communicating passagewaysparallel to the bottom face of the casting and extend ing through thethree bridges, and a bore leading to the passageways from the bottomface of the casting and exit bores leading from the connectedpassageways to the water space in the casting, whereby water willcirculate through the three connected passageways and provide thermalcontrol for the bridges.

2. The casting of claim 1 in which one of the passagewaysv extends fromone side face of the casting and two of the passageways extend from theopposite side face of the casting, the three passageways meeting at apoint roughly equidistant from the axes of the three recesses.

References Cited in the file of this patent UNITED STATES PATENTSJardine Oct. 6, 1942 Anderson et a1. Jan. 25, 1944 Sheppard Oct. 12,1948

